Kate, who was accompanied by her husband, was driven to St Mary's Hospital in central London. The couple had spent the weekend at Kensington Palace.
The Lindo Wing is where the late Princess Diana gave birth to William, 31, and to his younger brother Harry, 28, who will drop a place in the line of succession after the birth.
“Her Royal Highness the Duchess of Cambridge has been admitted this morning to St Mary's hospital, Paddington, London, in the early stages of labour. The duchess travelled by car from Kensington Palace to the Lindo wing at St Mary's hospital with the Duke of Cambridge,” Kensington Palace said in a brief statement.
Latest World News